西藏南部岗巴地区晚白垩世Cenomanian—Turonian集群灭绝事件后有孔虫动物群的复苏

西藏南部岗巴地区Cenomanian-Turonian界线附近发生过一次与大洋缺氧事件有关的集群灭绝事件。其后,随着海水中溶解氧含量的逐渐增加,海洋中微体古生物,尤其是有孔虫逐渐得到了恢复以至繁盛。从Turonian早期至Santonian晚期,有孔虫动物群的复苏过程经历了三个时期：残存期,复苏期及辐射期,其复苏的型式为渐变式复苏。     

Eocene carbonate clasts in Oligocene siliciclastic sediments of the Trapani Basin (NW Sicily): depositional and stratigraphic significance

The ‘Monte Bosco clays and quartz sandstones’, cropping out at Baglio Beatrice near Castellammare del Golfo (Sicily, southern Italy) and belonging to the Pre-Panormide domain, contain planktic and nannofossil assemblages indicating the lower Oligocene, whereas reworked larger foraminifers occurring in turbidites are upper Eocene, and limestone clasts scattered throughout the section and occurring in channelized conglomerates are lower Eocene (Cuisian) in age. The autochthonous benthic foraminiferal assemblages in the hemipelagic marly clay background sediment indicate a well-oxygenated sea floor and show a deepening-upward trend through the succession from a middle to lower bathyal zone. Turbidites are graded and the coarser fraction, at the base of the beds, is composed by scattered tests of shallow-water late Eocene foraminifers reworked into the Oligocene matrix dominated by planktic foraminifers. The latter dominate the finer fraction characterized by the occurrence of quartz grains. The analysis of six limestone clasts revealed the occurrence of four microfacies characterizing a shallow-marine moderate-energy environment, a high-energy vegetated shoal, a high-energy middle-ramp, and the outer-ramp. The investigated clasts are all of a similar age, middle Cuisian, according to the microfossils, which include alveolinids, ornatorotaliids, and Cuvillierina vallensis. The interpreted microfacies suggest a distally steepened ramp source area, although there is no outcrop of such a platform in NW Sicily. The ‘Monte Bosco clays and quartz sandstones’ were deposited along a slope periodically affected by turbidity currents and debris flows, which cannibalized cemented and unlithified Eocene shallow-water carbonate facies.     

Provenance analysis of Cenozoic conglomerates: Insights from Lower Cretaceous radiolarians in chert clasts from the Xigaze area,southern Tibet

Conglomerates, exposed on either side of the Yarlung Tsangpo suture zone (YTSZ) in southern Tibet, have attracted wide attention in elucidating uplift and erosion histories of the Himalayan-Tibetan orogen. However, the provenance of these conglomerates remains controversial. Although radiolarian-bearing chert clasts within these conglomerates have received little focus, identification of the radiolarian assemblages they contain could shed light on the provenance of these sedimentary units. We present the first report of Upper Jurassic to Lower Cretaceous (upper Kimmeridgian–lower Barremian) radiolarian assemblages recovered from chert clasts within the Liuqu and Gangrinboche conglomerates in the Xigaze area. To extract radiolarian fossils from independent clasts in the conglomerates, a detailed and efficient experimental process is illustrated. The assemblages are well correlated to those in the YTSZ and Tethyan Himalaya, showing typical Tethyan characteristics. The lithology of chert clasts and ages of constituent radiolarian faunas suggest that the chert clasts in Liuqu and Gangrinboche conglomerates were derived from the Bainang terrane. This interpretation implies that Early Cretaceous accretionary complexes in the YTSZ had been exposed and eroded before deposited as clasts in the Cenozoic Liuqu and Gangrinboche conglomerates.     

Taphonomic differentiation of Oxfordian ammonites from the Cracow Upland, Poland

Taphonomic analysis of Lower and Middle Oxfordian ammonites from the Cracow Upland, southern Poland (localities at Pod???e, Zalas, M?ynka) revealed differences in ammonite preservation. The studied ammonites, usually termed as external and internal moulds, show a more complex state of preservation. In the Middle Oxfordian glauconitic marls, ammonites are preserved as internal moulds with neomorphic calcite shells showing relics of the original internal structure. In the Middle Oxfordian platy peloidal limestones, ammonites are preserved mostly as external moulds, without septal suture, however under microscope might show relics of internal whorls and septa and/or subtle differences in sediment filling phragmocone chambers. In sponge–microbial bioherms and biostromes, ammonite internal moulds have shells, which in contrast to ammonites from glauconitic marls are not strictly neomorphic ones, but originated by shell dissolution and subsequent filling of moldic porosity by calcite cement. In sponge–microbial nodular limestones, the ammonites are strongly deformed and the outer wall is usually removed by dissolution under pressure. Other important taphonomic differences include the rate of compaction (highest in platy limestones), sedimentary infillings, microborings, encrustations and preservation of siphuncular tubes. The majority of the ammonites appear to be phragmocones; aptychi in all facies are rare. Siphuncular tubes are fossilized exclusively in oppeliids, only in specimens from glauconitic marls and platy limestones, although their other taphonomic attributes are different. Tubes seem to have fossilized due to microbially mediated phosphatization that could be favoured by a set of parameters which operated rather at the scale of ammonoid carcasses: closed, poorly oxygenated conditions, and reduced pH. Taphonomic processes were controlled by the sedimentary environment (fragmentation, sedimentary filling, phosphatization of siphuncular tubes), as well as by early and late diagenesis (neomorphic transformation, dissolution, cementation, compaction) influenced by lithology.     

Facies pattern and sea-level dynamics of the early Late Cretaceous transgression: a case study from the lower Danubian Cretaceous Group (Bavaria,southern Germany)

The facies development and onlap pattern of the lower Danubian Cretaceous Group (Bavaria, southern Germany) have been evaluated based on detailed logging, subdivision, and correlation of four key sections using an integrated stratigraphic approach as well as litho-, bio-, and microfacies analyses. Contrary to statements in the literature, the transgressive onlap of the Regensburg Formation started in the Regensburg–Kelheim area already in the early Early Cenomanian Mantelliceras mantelli ammonite Zone and not in the Late Cenomanian. In the Early Cenomanian, nearshore glauconitic-bioclastic sandstones prevailed (Saal Member), followed by Middle to lower Upper Cenomanian mid-shelf siliceous carbonates intercalated with fine-sandy to silty marls (Bad Abbach Member). Starting in the mid-Late Cenomanian (Metoicoceras geslinianum ammonite Zone), a considerable deepening pulse during the Cenomanian–Turonian Boundary Event (CTBE) initiated the deposition of the deeper shelf silty marls of the Eibrunn Formation, which range into the early Early Turonian. During the CTBE transgression, also the proximal Bodenwöhrer Senke (ca. 40 km NE of Regensburg) was flooded, indicated by the onlap of the Regensburg Formation onto Variscan granites of the Bohemian Massif, overlain by a thin tongue of lowermost Turonian Eibrunn Formation. A detailed record of the positive δ¹³C excursion of the global Oceanic Anoxic Event (OAE) 2 has been retrieved from this shallow-water setting. An integrated approach of bio-, event-, carbon stable isotope and sequence stratigraphy was applied to correlate the sections and to decipher the dynamics of this overall transgressive depositional system. The Cenomanian successions show five prominent unconformities, which correlate with those being known from basins in Europe and elsewhere, indicating their eustatic origin. The rate of sea-level rise during the CTBE suggests glacio-eustasy as a driving mechanism for Late Cenomanian sea-level changes. The Regensburg and Eibrunn formations of the lower Danubian Cretaceous Group are highly diachronous lithostratigraphic units. Their regional distribution and northeast-directed onlap pattern onto the southwestern margin of the Bohemian Massif can readily be explained by the lateral movements of roughly coast-parallel (i.e., NW/SE-trending) facies belts of a graded shelf system transgressing on a northeastward-rising substrate. It took the Cenomanian coastline ca. 6 Ma to transgress from southwest of Regensburg to the topographically elevated granite cliffs southeast of Roding in the Bodenwöhrer Senke (=60 km distance).     

Integrating palynological and geochemical data in a new approach to palaeoecological studies: Upper Cretaceous of the Banterwick Barn Chalk borehole, Berkshire, UK

The dinoflagellate cyst record from an Upper Cretaceous (uppermost Cenomanian–upper Coniacian) Chalk core, drilled at Banterwick Barn, Berkshire, is described and statistically correlated with elemental and stable isotope bulk sediment geochemical data from the same core. Seventy-two dinocyst species and subspecies are recorded, and stable carbon and oxygen isotopic (δ¹³C, δ¹⁸O) trends are documented. Lithostratigraphy and chemostratigraphic correlation of the δ¹³C curve with an expanded section at Dover, Kent, are used to identify stratigraphically significant marls, and determine the positions of macrofossil zones and stage boundaries in the Banterwick Barn core. These data indicate that >30 m of chalk at Dover are represented by <2 m of Chalk Rock at Banterwick Barn, with much of the succession being absent due to erosion and non-deposition. First and last appearance datums (FAD, LAD), first and last common occurrences, and acmes of key Turonian–Coniacian dinocyst species are documented and compared with other records from the Anglo–Paris Basin. A new subspecies, Senoniasphaera rotundata alveolata is proposed, which has a FAD in the lower Turonian and last appears (LAD) in the lower Coniacian. Senoniasphaera rotundata rotundata [autonym, herein] has its FAD in the middle Turonian, first common occurrence in the uppermost Turonian, and LAD in the upper Coniacian. An extremely impoverished assemblage of dinocysts in the highest Cenomanian to lowest Turonian is considered to be largely a preservational artefact of intraclastic nodular and calcarenitic chalks, and is not related directly to the well-documented global oceanic anoxic event (OAE2) occurring at that time (93.5 Ma). A sharp increase in dinocyst abundance in the lower Turonian corresponds with a change in lithology to more marly chalks. A gradual decrease in the number of species is observed through the middle Turonian to upper Coniacian; δ¹⁸O records show that this was associated with global climatic cooling. Cluster analysis of the dinocyst abundance record with geochemical data indicates four distinct species groups with characteristic geochemical associations, i.e. Groups 1–4. Groups 1 and 2 are associated with phases of increased siliciclastic supply; a positive correlation with higher δ¹³C values differentiates the latter. Group 3 is independent of carbonate and detrital input, and Group 4 is associated with high carbonate flux and low detrital supply. These groupings suggest that cyst-forming dinoflagellates exhibited a range of ecological niches in the Late Cretaceous. Although the relationship between the encystment process and the geochemical associations is unclear, key environmental factors are likely to be sea-level and climate related, including water depth, turbidity, nutrient supply, sea-surface temperature, and environmental stability/predictability. Integrated geochemical and palynological studies have great potential for inter-regional correlation and palaeoenvironmental interpretation.     

Turonian–Santonian radiolarians and planktonic foraminifers of the Upper Cretaceous sequences between Trabzon and Giresun areas in the Eastern Pontides,NE Turkey

In the “Eastern Pontides” (NE Turkey), the intense volcanic activity accompanying carbonate-siliceous sedimentation during the Late Cretaceous period ensured the occurrence of thick volcano-sedimentary sequences. Seventy-one radiolarian species belonging to 26 genera were identified from five stratigraphic sections of the Upper Cretaceous sequences between Trabzon and Giresun areas in NE Turkey. These species were obtained from the lower Turonian–lower Coniacian strata of the Çe?meler Formation, the Coniacian–lower Santonian strata of the Elmal? Dere Formation and the upper Santonian strata of the Ça?layan Formation. Coniacian–Campanian fauna, consisting of planktonic foraminifera Hedbergella, Marginotruncana, Globotruncana, Whiteinella and biserial heterohelicids as well as radiolarians, was recovered from the red pelagic limestones of the Elmal? Dere Formation known as marker horizon.     

Tectonically controlled late cretaceous terrestrial to neritic deposition (Northern Calcareous Alps, Tyrol, Austria)

Summary The Turonian to Santonian terrestrial to neritic succession (Lower Gosau Subgroup) in the Northern Calcareous Alps of the eastern part of the Tyrol, Austria, provides an example for deposition on a compartmentalized, narrow, microtidal to low-mesotidal, wave-dominated, mixed siliciclastic-carbonate shelf. The shelf was situated in front of a mainland with a relatively high, articulated relief, and underwent distinct changes in facies architecture mainly as a result of tectonism. The investigated succession was deposited above a deeply incised, articulated truncation surface that formed when the Eo-Alpine orogen, including the area of the future Northern Calcareous Alps, was uplifted and subaerially eroded. Distinct facies associations were deposited from (1) alluvial fans and fan deltas, (2) rivers, (3) siliciclastic lagoonal to freshwater marsh environments, (4) areally/temporally limited carbonate lagoons, (5) transgressive shores, (6) siliciclastic shelf environments, and (7) an aggrading carbonate shelf. During the Turonian to Coniacian, the combination of high rates of both subsidence and sediment accumulation, and a narrow shelf that was compartmentalized with respect to (a) morphology of the substratum, (b) fluviatile input of siliciclastics and contemporaneous input of carbonate clasts from fan deltas, (c) deposition of shallow-water carbonates, and (d) water energy and-depth gave rise to an exceptionally wide spectrum of facies as a distinguishing feature of the succession. With the exception of facies association 7, which formed only once, depositional sequences in the Turonian to Coniacian interval contain all of the facies associations 1 to 6. During Turonian to Coniacian times, the shelf was microtidal to low-mesotidal, and was dominated by waves, storm waves and storm-induced currents. In vegetated marshes, schizohaline to freshwater marl lakes existed. Transgressions occurred onto fan deltas and in association with estuaries, or in association with gravelly to rocky shores. The transgressive successions, including successions deposited from transgressive rocky carbonate shores, are overlain by regressive successions of shelf carbonates or shelf siliciclastics. Deposition of shallow-water carbonates generally occurred within lagoons and over short intervals of time. A „catch-up” succession of shelf carbonates about 100 m thick accumulated only in an area protected from siliciclastic input. In its preserved parts, the Turonian to Coniacian succession does not record deposition adjacent to major active faults. Lateral changes in thickness result mainly from onlap onto the articulated basal truncation surface. Subsidence most probably was controlled by major detachment faults outside the outcrop area, and/or was distributed over a wide area in association with secondary faults above the major detachments. During Coniacian to Early Santonian times, both the older substratum and the overlying Turonian-Coniacian succession were subaerially exposed, faulted and deeply eroded. The following Early Santonian transgression ensued with rocky carbonate shores ahead of a sandy, narrow shoreface-inner shelf environment and a deeper shelf with intermittentlydysaerobic mud. The transgression was associated with the influx of cooler and/or nutrient-rich waters, and heralds an overall deepening. Still during the Early Santonian, the deepening was interrupted by another phase of subaerial exposure. Subsequently, a short phase of shelf deposition was terminated by deepening into bathyal depths.     

Quaternary paleoceanology of Benguela upwelling based on microfossils (borehole 362 DSDP)

The study of the upper part of the section of borehole 362 DSDP (southeastern Atlantic) allowed the recognition of five zonal units in the Quaternary based on nannofossils and refinement of the UpperLower Pleistocene boundary based on benthic foraminifers. The study of planktonic and benthic foraminifers in sediments display the history of the Benguela upwelling. The temperature of the surface water layer reconstructed based on Upper Pleistocene planktonic foraminifers reaches 17°–19°C and decreases downward in the section to 2°–3°C, suggesting that, in the Early Pleistocene, the upwelling was more extensive in area. The increasing proportion of benthic foraminifers and large nannofossils downward in the section is evidence of more active dissolution of carbonates in the Early Pleistocene and the high content of terrigenous matter suggests that the Benguela Current occupied a westerly position. The existence of the Benguela upwelling throughout the Late Pliocene-Pleistocene was accompanied by a decrease in its activity.     

L’assemblage à Cardioceras (Cardioceras) cordatum (J. Sowerby, 1812) et sa place au sein de la succession ammonitique de l’Oxfordien Inférieur (Jurassique Supérieur). Apport des données ardennaises (Province Subboréale)

Some temporary outcrops at Villers-le-Tourneur/Neuvizy (Ardennes, France), made possible the observation and biostratigraphical dating of Uppermost Callovian to Early Middle Oxfordian poorly known formations. Especially, the “Oolite Ferrugineuse de Villers-le-Tourneur–Neuvizy” is a quite thick marly unit, yielding some silicified fossils well known since the XIX^th century. With details, the Formation displays the succession of several faunal associations, characterizing the main subzones of the Cordatum Zone (Late Lower Oxfordian) and the Plicatilis Zone (Early Middle Oxfordian). Amongst many other species, Cardioceras cordatum (Sowerby, 1812) corresponds to a rare taxon or morphotype, yielded by the bottom part of the Formation. Then, the ultimate Lower Oxfordian faunal association is dominated by ammonites related to C. persecans. These Early Oxfordian are widely dominated by the family Cardioceratidae, commonly associated with Aspidoceratidae; such a structure is related to the “subboreal associations”, typically represented in Great Britain. Immediately after the Middle Oxfordian boundary, some “subtethysian” ammonites (mainly Perisphinctidae), occur in a larger number without being dominant, that emphasizing the northern location of the Ardennes margin. Then locally, two faunal associations succeed, which are characterized by C. cordatiforme (with Euaspidoceras perarmatum), and C. densiplicatum, respectively. Both are typical associations of the Vertebrale Subzone (Early Middle Oxfordian).     

Late Cenomanian–Early Turonian facies development and sea-level changes in the Bodenwöhrer Senke (Danubian Cretaceous Group, Bavaria, Germany)

The Upper Cenomanian–Lower Turonian litho-stratigraphic units of the Danubian Cretaceous Group of the proximal Bodenwöhrer Senke (Regensburg, Eibrunn and Winzerberg formations, the latter consisting of a lower Reinhausen Member and an upper Knollensand Member), have been investigated with a focus on facies analysis and sequence stratigraphy. Analyses of litho-, bio-, and microfacies resulted in the recognition of 12 predominantly marine facies types for the Eibrunn and Winzerberg formations. Petrographic and paleontological properties as well as gradual transitions in the sections suggest that their depositional environment was a texturally graded, predominantly siliciclastic, storm-dominated shelf. The muddy–siliceous facies types FT 1–3 have been deposited below the storm wave-base in an outer shelf setting. Mid-shelf deposits are represented by fine- to medium-grained, bioturbated, partly glauconitic sandstones (FT 4–6). Coarse-grained, gravelly and/or shell-bearing sandstones (FT 7–10) developed in the inner shelf zone. Highly immature, arkosic coarse-grained sandstones and conglomerates (FT 11 and 12) characterize an incised, high-gradient braided river system. The Winzerberg Formation with its general coarsening- and thickening-upward trend reflects a regressive cycle culminating in a subaerial unconformity associated with a coarse-grained, gravelly unit of marine to fluvial origin known as the “Hornsand” which is demonstrably diachronous. The overlying Altenkreith Member of the Roding Formation signifies the onset of a new transgressive cycle in the early Middle Turonian. The sequence stratigraphic analysis suggests that the deposition of the Upper Cenomanian and Lower Turonian strata of the Bodenwöhrer Senke took place in a single cycle of third-order eustatic sea-level change between the major sequence boundaries SB Ce 5 (mid-Late Cenomanian) and SB Tu 1 (Early–Middle Turonian boundary interval). The southeastern part of the Bodenwöhrer Senke was flooded in the mid-Late Cenomanian (Praeactinocamax plenus transgression) and a second transgressive event occurred in the earliest Turonian. In the central and northwestern parts of the Bodenwöhrer Senke, however, the initial transgression occurred during the earliest Turonian, related to pre-transgression topography. Thus, the Regensburg and Eibrunn formations are increasingly condensed here and cannot be separated anymore. Following an earliest Turonian maximum flooding, the Lower Turonian Winzerberg Formation filled the available accommodation space, explaining its constant thickness of 35–40 m across the Bodenwöhrer Senke and excluding tectonic activity during this interval. Rapid sea-level fall at SB Tu 1 terminated this depositional sequence. This study shows that Late Cenomanian–Early Turonian deposition in the Bodenwöhrer Senke was governed by eustatic sea-level changes.     

Acicularia? weisswasserensis n. sp. and Terquemella? microsphaera n. sp., two new Dasycladales from the Upper Cretaceous (Late Turonian-Santonian) of the Northern Calcareous Alps (Gosau Group, Austria)

Two new dasycladalean algae are described from the Gosau Group of the Northern Calcareous Alps in Austria. The tiny spicules of Acicularia? weisswasserensis n. sp. were found in foraminiferal wacke- to packstones associated with rudist limestones of the Weisswasser locality (Middle Coniacian), Lower Austria. The small globulous Terquemella? microsphaera n. sp. occurs in marls to marly limestones of the Pletzachalm locality (Upper Turonian), Tyrol, and Russbach locality (Upper Santonian), Lower Austria. The Terquemella-Acicularia group requires taxonomic revision; the two forms described herein, however, are clearly distinct from other species, and belong to the smallest representatives of these genera. In addition, Acicularia? aff. magnapora Kuss and morphologically similar forms interpreted as gametophores of unknown larger dasycladales are described.     

<Emphasis Type="Italic">Crescentiella</Emphasis>-microbial-cement microframeworks in the Upper Jurassic reefs of the Crimean Peninsula

In the Upper Jurassic reef successions of the Crimean Peninsula (Sudak and Jalta areas), the microencruster Crescentiella morronensis (Crescenti), microbialites, and multiple generations of cements, form microframeworks. They were observed in two stages of the carbonate platform evolution, in the Middle–Upper Oxfordian, and in the Upper Kimmeridgian–Tithonian. Generally, in both stages, the features of the microframeworks are similar and consist of densely packed Crescentiella associated with microbialites and branched colonies of the sclerosponge Neuropora lusitanica Termier. The difference between the occurrences of the two stages is the variable amount of nubecularid foraminifera and enigmatic tube-shaped structures forming the central cavities of Crescentiella. The Crescentiella-microbial-cement microframeworks formed under phreatic conditions in the upper slope and seaward marginal depositional settings where intensive synsedimentary cementation took place. They formed in the initial stages of long cycles of restoration and blooming of the reefs. The late Jurassic examples resemble the Permian algae-microbial-cement reefs as well as the Triassic Tubiphytes and cement crust-dominated reefs. Concurrently, all these examples formed a transitional facies zone between typical slope facies to shallow subtidal platform margin facies characterized by high taxonomic diversity of calcified sponges, corals, and microencrusters forming the principal part of the reefs.     

Tithonia oxfordiana,a new irregular echinoid associated with Jurassic seep deposits in south‐east France

Abstract: The infaunal irregular echinoid, Tithonia oxfordiana, is described and compared to congeneric species previously described from Upper Jurassic and lowermost Cretaceous strata. This new species characterizes a monospecific echinoid assemblage, which occurs only in some places where deep‐marine middle Oxfordian deposits are exposed in south‐east France. Specimens are closely packed and clearly concentrated at the top of small carbonate chemoherms; a close connection of the echinoids with the emission of reduced chemicals, which were oxidized by chemoautotrophic bacteria, is highly probable. Based on general test shape and plate architecture, T. oxfordiana probably was a deposit feeder on chemosynthetic organic matter produced by such bacteria. In view of the fact that T. oxfordiana is the sole species of the Jurassic genus Tithonia known from Oxfordian strata, it is postulated that chemoherms possibly acted as refugia for these peculiar echinoids, which have an episodic record between the Callovian and Valanginian.     

Episodic sedimentation on a peri-Tethyan ridge through the Middle–Late Jurassic transition (Villány Mountains, southern Hungary)

The Villány area, as a central part of the Tisza microcontinent/terrane along the European margin of Tethys, was characterized by intense subsidence in the Early and Middle Triassic, followed by a long interruption of subsidence in the Late Triassic to Middle Jurassic. During the Middle–Late Jurassic transition, marine sedimentation started with three distinct sedimentary episodes dated as Late Bathonian, Early Callovian, and Middle–Late Callovian, respectively. The succession is terminated by a thick limestone of Middle Oxfordian age. The sedimentary features, microfacies, and macroinvertebrate associations of these four stratigraphic units are documented and illustrated. The Middle to Late Jurassic sedimentary episodes of the Villány succession record an interplay of local and global factors and paleogeographical changes. At the beginning, local tectonic movements governed the main features of sedimentation, though the role of eustasy was also essential. From the mid-Callovian onwards, global climatic, biotic, and paleoceanographical changes controlled the nature and formation of the local carbonate sediments. The Callovian stromatolites are attributed to the activity of sulphate-reducing bacteria in a deep sublittoral, current-swept environment. Upwelling of eutrophic Tethyan waters is recorded by the prevalence of the Bositra filament microfacies in the Callovian. The long submarine hiatus at around the Callovian–Oxfordian transition mirrors a serious restriction of the carbonate budget, due to sudden cooling and a change in the oceanic current system (opening of a circumglobal Tethyan Passage), and to a higher amount of dissolved CO₂. In the Middle Oxfordian, the carbonate production considerably increased in accordance with the sudden global warming.     

Les Gregoryceras (Ammonitina) de l’Oxfordien moyen terminal et supérieur téthysien : révision systématique, biostratigraphie et évolution

In prolongation of the previous studies, the Gregoryceras Spath, 1924 (Ammonitina, Peltoceratina) species from the uppermost Middle Oxfordian (Rotoides sub-zone) to the Early Late Oxfordian (Bifurcatus zone), are revised. Sections providing most of the studied specimens in this work (Spain, Algeria, Tunisia) are described and dated based on faunal comparisons between Tethyan and Subtethyan domains. It appears that the best tool for correlations is the presence of the genus Gregoryceras, the succession of its species being similar for the two considered domains. It allows us to complete the biostratigraphic scale based on the Gregoryceras species succession, and parallel to the standard zonation. During this period the revised species of Gregoryceras are G. fouquei (Kilian, 1889) and G. pervinquieri (Spath, 1913). G. fouquei is only present in the Rotoides sub-zone (uppermost Middle Oxfordian), and not in the Stenocycloides sub-zone (early Late Oxfordian), where G. pervinquieri (Spath, 1913). A new species, G. benosmanae nov. sp. is described as the most recent species of the genus (Grossouvrei sub-zone). The evolution of the youngest species of Gregoryceras continues the peramorphocline described for older forms. Concerning a potential dimorphism, new data (size differences, umbilicus enlargement during growth) are particularly provided by G. pervinquieri.     

Permian and Triassic radiolarians from chert breccia in the Nong Prue area,western Thailand: its origin and depositional setting in the Paleotethys

Bedded chert and siliceous shale successions previously regarded as the Silurian–Devonian rock units, distributed in the Nong Prue area, northwest of Kanchanaburi, western Thailand, yielded Lopingian (upper Permian) and Lower–Middle Triassic radiolarians. We found chert breccia layers in northern Nong Prue area, mainly consisting of angular to sub-angular chert clasts with matrices of silt-sized chert grains and clay minerals. We discriminated uppermost Pennsylvanian–Lopingian (upper Carboniferous–upper Permian) and Middle Triassic radiolarian-bearing chert clasts from four different levels of the chert breccia; 28 species of 15 genera with one radiolarian gen. et sp. indet. are identified. On the basis of sedimentary characteristics of the chert breccia, we suggest that the chert breccia is of sedimentary origin. The radiolarian assemblages reported here, together with previously known lithological and paleontological evidence, further indicate that the chert breccia was deposited in the Paleotethys with chert clasts derived from fine grained siliceous rocks in the continental margin to deep ocean basin of the Sibumasu Terrane.     

Cyrtocrinids (Crinoidea) and associated stalked crinoids from the Lower/Middle Oxfordian (Upper Jurassic) shelfal deposits of southern Poland

Five cyrtocrinid crinoid taxa previously unknown from the epicratonic deposits of Poland, as well as associated millericrinids and isocrinids, are described. The studied materials were derived mainly from the Lower and Middle Oxfordian, but crinoids are also from uppermost Callovian and/or lowermost Oxfordian sediments of the Polish Jura Chain (southern Poland). The crinoids, preserved as more or less complete (e.g., basal circlets) cups, include Lonchocrinus dumortieri, Phyllocrinus belbekensis, Remisovicrinus polonicus, Remisovicrinus aff. polonicus, Tetracrinus moniliformis and Sclerocrinus sp. The occurrence of Remisovicrinus polonicus in the late Middle Oxfordian of the southern Poland is confirmed. Moreover, the present study extends the geographic range of all cyrtocrinid species studied and discusses their unusual environmental adaptations.     

Platform-basin transect of a middle to late Jurassic large-scale carbonate platform system (Shotori mountains,Tabas area,east-central Iran)

Summary Following a phase of predominantly siliciclastic sedimentation in the Early and Middle Jurassic, a large-scale, low-latitude carbonate depositional system was established in the northern part of the Tabas Block, part of the central-east Iranian microplate, during the Callovian and persisted until the latest Oxfordian/Early Kimmeridgian. Running parallel to the present eastern block margin, a NNW/SSE-trending carbonate platform developed in an area characterized by reduced subsidence rates (Shotori Swell). The growth of this rimmed, flat-topped barrier platform strongly influenced the Upper Jurassic facies pattern and sedimentary history of the Tabas Block. The platform sediments, represented by the predominantly fine-grained carbonates of the Esfandiar Limestone Formation, pass eastward into slope to basin sediments of the Qal'eh Dokhtar Limestone Formation (platform-derived allochthonites, microbialites, and peri-platform muds). Towards the west, they interfinger with bedded limestones and marlstones (Kamar-e-Mehdi Formation), which were deposited in an extensive shelf lagoon. In a N−S direction, the Esfandiar Platform can be traced for about 170 km, in an E-W direction, the platform extended for at least 35–40 km. The width of the eastern slope of the platform is estimated at 10–15 km, the width of the western shelf lagoon varied considerably (>20–80 km). During the Late Callovian to Middle Oxfordian, the Esfandiar Platform flourished under arid climatic conditions and supplied the slope and basinal areas with large amounts of carbonates (suspended peri-platform muds and gravitational sediments). Export pulses of platform material, e.g. ooids and aggregate grains, into the slope and basinal system are interpreted as highstand shedding related to relative sealevel variations. The high-productivity phase was terminated in the Late Oxfordian when the eastern platform areas drowned and homogeneous deep water marls of the Upper Oxfordian to Kimmeridgian Korond Formation onlapped both the Qal'eh Dokhtar Limestone Formation and the drowned Esfandiar Limestone Formation. Tectonic instability, probably caused by faulting at the margins of the Tabas Block in connection with rotational movements of the east-central Iranian block assemblage, was responsible for the partial drowning of the eastern platform areas. In some areas, relicts of the platform persisted to produce shallow-water sediments into the Kimmeridgian.